This invention relates to a method of securing a curing composite wrap material wrapped about a structure. In particular, this invention relates to securing a substrate to a cylindrical or rectangular block structure, such as a pipe, or column, using at least one strap with clips to hook into and connect the substrate to an overlapping layer of substrate, thereby affecting a repair both by allowing the substrate to cure without peeling away from the pipe, column or structure and by creating additional tension on the substrate during the cure cycle. An end edge of the substrate may be more firmly secured along its full length by placing a plastic bar under the strap.
Pipe systems provide basic utilities to the public, such as water, gas, petroleum, and sewage. These basic utilities and petroleum pipeline operators are often heavily relied upon by the public. As such, the pipe systems are usually in a state of full operation, i.e. optimal flow rate.
Pipelines and other cylindrical or rectangular block structures, whether above ground or below, submerged or partially submerged, occasionally suffer damage. Over time, these structures can be damaged from rust, corrosion or other degradation. The damage can also occur during repair or installation of the structure, for example from tool impact or falling debris.
The damage to the pipe usually results in a reduced flow rate. At the damaged area of the pipe, there is a smaller cross-sectional thickness of the pipe. The thickness of the pipe is inversely proportional to the hoop stress of the pipe, i.e. the circumferential stress in the pipe due to the operational fluid pressures in the pipe. Accordingly, there is a larger hoop stress in the damaged area as compared to the rest of the pipe.
The hoop stress in the pipe is proportional to the strain in the pipe. Therefore, the larger hoop stress in the damaged area results in a proportionally larger strain. The larger strain in the damaged area of the pipe causes further damage. Consequently, to minimize the potential damage to the pipe, the pressure in the pipe is lowered which reduces the flow through the pipe until the pipe is repaired or replaced. However, flow reduction is undesirable because the utility service is correspondingly reduced. There is usually a very limited amount of time that the pipes and pipe systems can operate at the reduced flow rate, while not seriously affecting utility service.
It is often more cost effective to permanently repair the leaking or damaged pipe rather than replace it. When the damaged pipe is replaced, the downtime of the system, the labor costs, the material costs, as well as the costs associated with the loss of utility services are often large.
An expedient method of repair involves, at least in part, applying a structural reinforcement by way of wrapping the structure with a flexible repair substrate. Such flexible substrates are commonly tapes (defined principally by films), woven fabrics, and non-woven fabrics. Non-woven fabrics are characterized by the non-parallel, random organization of the component fibers, for example, paper. The flexible substrates are often used in conjunction with various adhesives, resins, putties, and fill materials. The sum of the various components is a composite substrate. The composite substrate is wrapped about the pipe while the substrate is curing.
The flexible repair substrate has a characteristic tensile strength of its own. In the finished repair, the substrate is pulled or tensioned in several turns about the pipe, thus applying to the pipe a compressive force pattern which acts counter to hoop stresses created by fluid pressure in the pipe.
Because of the tight substrate wrap about the pipe, when the pipe is strained by internal fluid pressure, the repair substrate also strains proportionally to share hoop stress with the pipe. This method of repair keeps the strain and stress in the damaged area of the pipe within acceptable limits when full operational fluid pressures are applied within the pipe. If one layer of substrate cannot withstand the tension created by the shared hoop stress, additional or thicker layers of substrate are added. Overlapping adjacent layers of substrate and/or wrapping additional layers of substrate over the damaged area of the pipe provide the thicker substrate layers, and thus more strength in the repair. The overlap of the adjacent layers renders the substrate being angled relative to the central axis of the structure, or having a spiral-shape or helix-shape wrapping material about the structure. With a low helix pitch, there is a greater the amount of overlapping substrate. Conversely, with a greater helix pitch, there is a lesser amount of substrate that overlaps.
After the composite substrate is wrapped about pipe, the substrate is typically still in a state of curing. At this point, depending upon the curing stage, there is a possibility that an end edge of the substrate may not adhere to the previously wrapped layer of substrate. The end edge of the substrate then begins to peel back unless the operator holds the substrate end edge until adherence. If the end edge peels away from the pipe, the substrate will finish curing in this position, that is, where the end edge of the substrate is not in contact with the previously wrapped layer of substrate. If cured in this position, the substrate end edge will no longer be able to adhere to the previously wrapped substrate, and the repair will be compromised. In underwater applications water flow, from tides, for example, may cause the composite substrate to unwind before it cures.
The most common structures that are repaired by way of wrapping with a flexible substrate are cylindrical or rectangular box structures, such as utility poles, architectural and industrial support columns, and pipes. However, other shaped structures, with both regular and irregular cross-section, can also often be advantageously repaired by way of wrapping the structure with a flexible reinforcing substrate. Structures that may need repair may be comprised of metal, concrete, composites, fiberglass, and plastics, including polyethylene, PVC, and polyurethane.
A pressurized vessel or pipe is operated in a pressurized fluid system. A fluid in the pressurized vessel is intended to be present at a predetermined pressure. The vessel has a wall that has a condition (i.e., damage) in a localized area that creates a hoop stress that is greater than the pipe""s design hoop stress at the design fluid pressure. To prevent further damage to the pipe, a flexible composite substrate is tightly wrapped and secured around the localized area of the pipe. The substrate thereby reduces the hoop stress in the localized area of the pipe.
The wrapped and curing substrate is secured with a strap. The strap has two elastically connected clips, each having prongs. The prongs of a first clip are slid in a first direction into a first portion of the wrapped substrate. A second clip is pulled away from the first clip over a substrate edge, and the prongs of the second clip are slid into a second portion of the wrapped substrate in a direction opposite the first direction. In addition to avoiding an unravel of the substrate while the substrate is curing, the clips may also add tension to the substrate. Additional holding power can be applied using several straps. Alternatively, or in addition, a tension bar is applied across the end edge of the curing substrate under the straps. The straps and/or the tension bar may be removed after cure or remain to provide the additional tensile force.
In one embodiment, the first portion of the wrapped substrate is an overlapping layer of substrate, and the second portion of the wrapped substrate is the layer of substrate protruding from underneath the overlapping substrate.